Mutational and gene dosage analysis of calcium-activated potassium channels in Drosophila: Correlation of micro- and macroscopic currents

In Drosophila, two Ca²⁺-activated K⁺ currents, I_CF and I_CS, have previously been distinguished in conventional voltage clamp experiments. The slowpoke(slo) mutation eliminates IcF specifically. We report that in patch clamp recordings a single-channel Ca²⁺-activated K+ current is readily distinguished from other channel activities in normal larval muscle membrane, whereas no such current is observed in slo muscles. This single channel current thus correlates with the macroscopic I_CF. No obvious differences in amplitude or properties were detected between normal (+/+) and heterozygous (slo/+) I_CF channels in whole-cell voltage clamp recordings or single-channel patch clamp recordings. These results are consistent with the hypothesis that slo is a structural gene for the IcF channels only under certain conditions. The selective effect of the slo mutation may reflect a defect in a regulatory mechanism that is specific for the functioning of the IcF channel protein.